Baron Humboldt has addressed a letter from Berlin to the Academie des Sciences of Paris.

The following is a copy:--

Monsieur le President--The generous interest which the Institute has taken, in its sittings, whenever the name of my friend and travelling companion, M. Bonpland , has been mentioned--the kind feeling with which the Academy has deigned to associate itself to the fruitless attempts which ought to have accelerated the release of this learned man, imposes on me the duty of addressing these lines to you.

More than twelve months had elapsed since the first news of the arrival of M. Bonpland in the Provincia de las Missiones: no letter from him had come to Europe, and my uneasiness was shared with his relations, who reside at Rochelle; at last I was fortunate enough to receive news direct, by means of M. le Baron Delessert.

A letter from M. Bonpland , dated Buenos Ayres, May 7, 1832, informs me that he had in January received a letter which I had written to him from Paris about the end of July last year, during his stay at Corrientes, near the conflux of the rivers Parara and Paraguay.

"I have been thwarted, he says, in all the projects I had formed on quitting France.

An evil star has followed me for fifteen years.

I hope that my lot will be more fortunate now that I have quitted Paraguay.

Restored to my friends, and in communication again with civilization and with Europe, I have resumed my researches in natural history with the greatest activity, in order to return as soon as possible to my native land.

My collections at Paraguay and the Portuguese mission ought to have arrived at Buenos Ayres in the month of March.

I expect them with great uneasiness, and I shall expedite them as soon as they arrive, which cannot be long, under address to the Minister for Foreign Affairs at Paris, with a request to the Minister to cause the chests to be forwarded to the Museum of Natural History.

"The Jardin des Plantes will not only receive what I have gathered recently, but also such herbs as I have saved at Corrientes and at Buenos Ayres, particularly my herbier general and the suite geoligique of the course of our travels.

"I will add to the collection some geological specimens which I have already gathered, and also such as I may procure in a few days in my excursions to Monte Video, Maldonado, and Cabo-Santa-Maria.

"Here I live in the house of M. le Chev.

de Angelis, a Neapolitan, who has received me with the greatest hospitality, and whom you have seen at Paris in the society of Madame the Comtesse Orloff. I find every facility in expediting my collections to France.

"The fertility of the soil, and the richness of vegetation in the Portuguese settlements are such, that I think of returning there: I think that those who wish to interest themselves in my speedy return to Europe, will not disapprove of this journey.

It would be cruel to leave without enriching Botany with so many remarkable productions.

My collections contain two new kinds of convolvulus, the roots of which have all the fine qualities of the salep. I hope also that the Medical School will make some experiments upon three new sorts of Bark, very bitter, belonging to the genus simaroubus.

These barks have the taste of sulphate of quinine, and act with great effect in complaints of the stomach and dysenteries.

If I could still obtain information respecting the efficacy of these barks, after a trial at Paris, I should try, before my departure, to make arrangements for the supply of our hospitals."

Such is the information which I have considered it my duty to extract from the letter of M. Bonpland , and I have to regret other letters previously written and probably lost.

I take this opportunity to communicate to the academy a geological fact, with which we have only been acquainted for a few days, and which forms a link to other facts observed in Europe, and even in the interior of Asia. M. de Seckendorf has found in Hartz (valley of Radan), in a quarry near the highway leading to Hartzbourg, fragments of grawakke, with petrification empatee dans le granit.

The translator of Geologie de Lyel, M. Hartman, has confirmed the accuracy of this information, and announces that he will shortly send me specimens, carefully detached by regular work of art, a la paintrole.

Berlin, Aug. 26, 1832. I have, &c &c.